For illustration, VDDmin is the minimum value of a supply voltage VDD to be provided to a memory cell, and VDDmax is the maximum value of the supply voltage VDD to be provided to the memory cell. In some approaches, a memory cell comprises two read-write ports, and is specified to function when the supply voltage VDD is within a range of VDDmin and VDDmax value. For simplicity, a read-write port is called a port.
A write disturb occurs, for example, when a first port is used to write to the memory cell and is disturbed by a “dummy” read from the second port of the same memory cell. A dummy read refers to a situation in which signals for the port are in a read condition, but the data is not reliable, and therefore is not used. Generally, the dummy read from the second port increases a load on a storage node to be written, and thus prolongs the write time from the first port.
In many situations, when a write disturb occurs, the write operation cannot operate at VDDmin value. In some application, a write assist circuit is turned on so that the write operation and the memory cell continue to function at VDDmin value. In some designs, the write assist circuit consumes about 20% of the total active power of the memory cell. Further, the write assist circuit is turned on every time the memory cell is write-accessed, which increases power consumption of the memory cell.
Like reference symbols in the various drawings indicate like elements.